This invention relates generally to a shock attenuating apparatus and a related shock attenuating method. The invention relates more particularly, but not by way of limitation, to a mandrel and a method for attenuating an explosion-created impact load and its resultant shock wave in a tool string within a well.
When a collection of components are strung together, sometimes one section of components needs to be buffered from another section of components so that shock forces from one section do not travel into the other section with a sufficient intensity to cause damage. By way of example, in an oil or gas well, casing or tubing located in the well sometimes needs to be cut. One way of doing this is to lower a tubing or casing cutter containing explosives into the well to the point at which the cut is to be made. The explosive is then detonated. Although the force from the explosion is intended to be directed towards the tubing or casing, an impact load from the explosion tends to lift the tool string. Furthermore, the impact load includes one or more shock waves which are conducted up the tool string by which the cutter is lowered into the well. A typical tool string also contains working components such as a casing collar locator. These working components can be sensitive to, and damaged by, the impact load (particularly its shock wave) which is produced by the cutter explosion.
To try to attenuate an impact load shock wave before it reaches other components, long sections of pipe or tubing have been connected into the tool string between the cutter and the other components. It is intended that the shock wave be damped by the resistance of the long pipe section.
Although such long pipe section helps to attenuate the shock, we believe that better shock attenuation can be obtained. Additionally, a long pipe section is cumbersome and it adds to the length and weight of the tool string. Therefore, there is the need for an improved apparatus and method for attenuating shock such as is created by the explosion of a tubing or casing cutter downhole in an oil or ga well.